In many undeveloped areas and undeveloped countries, wireless communications offers a sensible method of providing communications without the need for major expenditures of funds for outside-plant communications infrastructure, e.g., telephone poles, lines, and other facilities. However, even with certain so-called fixed “wireless” systems, some communications wiring is still required within a home or business so that communications devices, such as telephones, facsimile machines, and computers, can be connected to the fixed wireless terminal serving that home or business. Once communications between the devices and the wireless terminal is established, the wireless terminal communicates in a true wireless fashion to other wireless terminals or to a base station thereby avoiding the more extensive outside-plant communications infrastructure.
The installation of communications wiring and equipment, in order to interface the home or business with a wireless system, is a significant cost for a household or business, one which often deters those in undeveloped countries from wiring households or businesses for wireless communications.
However, unlike outside-plant communications infrastructure and communications wiring which has not been extensively installed, electrical power in various forms has reached many homes throughout the world via power lines. Therefore, in many third-world countries, power wiring interfaced with power lines may exist within a home or business, even though communications wiring might not.
Systems have been developed which couple telecommunications signals to a power distribution system. These systems utilize the power wires for the transmission of communications data and signals. Thus, these systems overcome the need to install communication wiring and equipment in providing a home or business with communications capabilities.
These systems generally entail a power line network architecture having a transmitter and a receiver designed to transfer a large amount of data from point-to-point, i.e., from one or more sources to one receiver, using bi-directional multiplexing. For multi-point networks, a time division multiple access (TDMA) protocol is often utilized. In such a multi-point network, each “packet” of information is multiplexed by a transmitter in a time sequence on a power line. A receiver at a central node must handle each packet as a burst of data coming from multiple sources where the packets have a wide range of input powers.
Preferably, such a receiver should have a wide dynamic range, high sensitivity and minimum inter packet idle time (IPIT) between any two adjacent packets having a high adjacent packet power ratio (APPR). The receiver should be able to handle non-synchronous packets of high APPR, separated by a small amount of time. An ideal IPIT is one nonretum-to-zero (NRZ) data bit in length (time) and is equal to 2×Tb, where (½×Tb) is a data clock frequency.
A receiver used to receive such bursts of data, hereafter a “burst mode receiver”, must be able to overcome a number of difficulties. First, extracting timing information from incoming data is difficult to do. Second, tracking maximum and minimum voltage swings on a real-time basis in order to utilize decision threshold is also difficult. No amount of circuit training can aid in decision extraction without real-time signal processing. Third, the receiver must be able to eliminate unwanted high-energy power line frequencies, remove spectral shaping for NRZ-coded data, and eliminate pulse width distortion resulting from APPR. Fourth, the receiver has to receive packets of smaller signal power amplitude in the presence of large background DC frequencies or power line frequencies.
Most conventional receivers used in coupling data to power lines use AC coupling. Coupling capacitors used in existing AC coupled systems are examples of real-time processors which establish ideal thresholds after a few pulses. However, coupling capacitors introduce base line “wander” problems due to long strings of “1”s or “0”s in NRZ data packets, typically used in coupling data to power line networks.
Further, there exist other major disadvantages in using a power distribution network or power transmission network for the transmission of communications data. One major disadvantage is the interference of the communications data and signals by electromotive and electrostatic forces present in a typical power line. Another major disadvantage is the adverse effect that out-of-band DC and low frequencies inherent in the power line, as well as carrier frequencies and their harmonics present in the power line, have on communications data and signals propagating through the power line. Yet, another major disadvantage is that the communications data and signals are not by design inserted at a point along the power spectrum having the minimum interference. Further still, another major disadvantage is the sipping of frequencies and associated harmonics of communications data and signals into the power line, thereby affecting the power spectrum. Finally, another major disadvantage is the inability of prior art power line communication systems to use base-band communications data and telephone messages, since they use carrier modulation schemes. The carrier is on most of the time, either modulated with data or unmodulated. The total amount of undesired electrical interference thus increases with prior art power lines.
Also, power line usage with masers makes the power line susceptible to magnetic field interference, thereby creating signal strength variations. Masers can also be problematic in hospitals using MRI machines and other magnetic sensors, such as Hall effect sensors.